A typical conventional damping brace may include a steel axial force member, a constraining member for preventing buckling of the axial force member, and an adhesion preventive coating for preventing adhesion between the constraining member and the axial force member. The axial force member may include a yielding part for deforming yielding when a tensile force or a compressive force that exceeds a specified magnitude is applied, a stiffening part for stiffening an end of the axial force member that protrudes from the constraining member, being covered together with the yielding part by the constraining member, and a joint part that is jointed to the structure.
The damping brace is generally installed diagonally in the plane of the structure, which is constructed in a rectangular shape by columns and beams, where each end of the axial force member is fastened to a welded gusset plate with bolts.
When a vibrational energy due to earthquakes, winds or the like is applied to a structure that may include the damping brace, a tensile force or a compressive force is applied on the axial force member, whereupon the yielding part deforms in the tensile direction (or a compressive direction), and in this manner absorbing the energy.
Studies concerning such a damping brace have been made to prevent local buckling of the axial force member by specifying the thickness and stiffness of the coating that prevents the adhesion between the hardened concrete and the axial force member as described by Japanese Patent Application 2001-227192, the entire disclosure of which is incorporated herein by reference.
In addition, the above-type arrangements generally undergo various studies and tests to verify whether they would deform according to the expected parameters in response to vibrational energy. However, generally, no verification is performed with regard to a buckling deformation of the joint between the damping brace and the structure. It has been ascertained that, in order to have the damping brace produce a damping effect according to expected parameters, it may be important to clarify the problem of the hinge phenomenon that occurs at the external portion(s) of the axial force member when the damping brace is subjected to compressive forces. If one or more external portion(s) of the axial force member undergo a hinge phenomenon and exhibit unstable behavior, the damping brace would likely not be designed to have the stiffness and yield strength, and may become unable to adequately absorb the vibrational energy.
Such hinge phenomenon is shown in FIGS. 17(A)–17(C). As shown in FIG. 17(A), a damping brace 100 is equipped with an axial force member 101 and a constraining member 102. The axial member 101 has a yielding part 103 and a stiffening part 104.
When excessive compressive forces act on damping brace 100, an end of axial force member 101 protruding from constraining member 102 (i.e., the part stiffened by stiffening part 104) may deform in a direction outside the plane of the structure frame (i.e., a direction perpendicular to the plane of the structure). In particular, as shown in FIG. 17(B) and FIG. 17(C), the end of axial force member 101 deforms as if a hinge rotates around the area of the boundary between yielding part 103 and stiffening part 104, while compressing the adhesion preventive coating (not shown). This phenomenon is generally referred to as the hinge phenomenon and the condition wherein a yielding is caused in the end of axial force member 101 to cause it to bend is expressed as “a hinge H is formed.”
The hinge phenomenon in the vicinity of the boundary between yielding part 103 and stiffening part 104 does not actually occur as long as the joint part between the end of axial force member 101 and gusset plate 110 has a sufficient stiffness, but a similar hinge phenomenon can occur surrounding the boundary area between the end of axial force member 101 and gusset plate 110 if a compressive force exceeding the stiffness of this part is applied. Under a condition where hinge phenomena can occur in the vicinity of the boundary between yielding part 103 and stiffening part 104, as well as the end of axial force member 1101 and gusset plate 110, three or four hinges H can be formed in damping brace 100, making the performance of damping brace 100 unstable.